This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Early biomarkers of skeletal muscle anabolism will facilitate development of therapies for sarcopenia and frailty. Using transcriptome and proteome profiling, and 13C6-Leu incorporation into muscle proteins, we examined plasma type III collagen N-terminal propeptide (P3NP), skeletal muscle protein fractional synthesis rate, gene and protein expression profiles to identify testosterone-induced changes in muscle anabolism. Two placebo-controlled studies enrolled community-dwelling men (Study 1, 60-75 years;Study 2, 18-40 years) with low-to-normal testosterone levels. Men were randomized to lower-dose (Study 1: 100 mg;Study 2: 200 mg) or higher-dose (Study 2: 300 mg;Study 2: 600 mg) single intramuscular testosterone or saline injection.